In this field, it is common to servo-control the orientation of the solar tracker based on an astronomical calculation of the position of the Sun, for a real-time positioning facing the Sun.
However, this servo-control type has a major drawback by offering a yield deficit under certain meteorological conditions, and we will advantageously refer to FIG. 1 for explanation; this FIG. 1 including four diagrams (1a), (1b), (1c) and (1d) each illustrating two solar trackers ST under different meteorological conditions, with the Sun SO always at the same position and with the solar trackers ST always orientated facing the Sun.
The diagram (1a) illustrates ideal meteorological conditions, in the absence of clouds, and the solar trackers ST are orientated facing the Sun SO in order to benefit from a maximum direct solar radiation Rdir. Under these optimum conditions with a zero-cloud coverage, the servo-control on the position of the Sun SO provides a maximum operation; such a servo-control corresponding to a servo-control of the orientation of the solar tracker on an inclination angle called direct inclination angle defined by the direction of the direct solar radiation Rdir at the solar tracker.
The diagrams (1b), (1c) and (1d) illustrate degraded meteorological conditions, with different cloud coverages depending in particular on the cloudy surface or overcast surface, the types of present clouds NU, the number and the position of the clouds NU in front of the Sun SO.
Under such cloudy conditions, the servo-control on the position of the Sun SO may not provide the best yield, when not considering the diffuse solar radiation Rdif. The diffuse solar radiation Rdif arises when the direct solar radiation Rdir is dispersed in the clouds NU and the atmospheric particles. The diffuse solar radiation Rdif results from the diffraction of light by the clouds NU and by the various molecules in suspension in the atmosphere. Hence, the diffuse solar radiation Rdif does not necessarily follow the direction defined by the Sun SO in the direction of the observation point at the Earth's surface.
Consequently, under cloudy conditions, it may be preferable, in order to obtain a maximum yield with regards to these conditions, to orientate the solar trackers ST in an orientation called indirect or diffuse orientation according to a direction of the diffuse solar radiation Rdif which does not necessarily correspond to the direction of the direct solar radiation Rdir; such a servo-control corresponding to a servo-control of the orientation of the solar tracker on an inclination angle called diffuse inclination angle defined by the direction of the diffuse solar radiation Rdif at the solar tracker.
In the diagrams (1b), (1c) and (1d), all the solar trackers ST are orientated according to the direct inclination angle (facing the Sun) while orientations according to diffuse inclination angles would offer better yields.
Thus, those skilled in the art would be inclined to servo-control, in real-time, the orientation of the solar tracker on an optimum inclination angle corresponding to a maximum solar radiation. In the absence of clouds, the optimum inclination angle would correspond to the direct inclination angle and, in the presence of a cloudy coverage and even one single cloud in front of the Sun, the optimum inclination angle would correspond to a diffuse inclination angle. For this purpose, it would be sufficient to measure the magnitude of the radiation at different directions (or different inclinations), and establish the direction corresponding to a maximum magnitude in order to deduce the optimum inclination angle.
However, proceeding in this manner would have numerous drawbacks, all of them relating to the variation of the diffuse solar radiation over time. Indeed, depending on the time evolution of the cloud layer (because of the displacement of the clouds under the effect of the winds) and depending on the composition of this cloud layer (number, dimensions, location and types of clouds), the diffuse solar radiation may vary more or less rapidly and therefore the optimum inclination angle may vary more or less quickly over time.
Thus, by servo-controlling the orientation of the solar tracker on this optimum inclination angle, the solar tracker may be brought to change its orientation more or less frequently and more or less quickly. Yet, each orientation change urges at least one actuator (an electric motor in general), resulting in an electrical consumption and wear of the mechanical members loaded by the orientation change (members of the motor, bearings, rotation guide elements . . . ). These electrical consumptions and these wears will not necessarily be compensated by the gains in productivity when switching in real-time on the optimum inclination angle.
As example, starting from an initial situation where the optimum inclination angle corresponds to the direct inclination angle (because of the absence of clouds between the Sun and the solar tracker), if one single cloud passes in front of the Sun for a few minutes, the optimum inclination angle will be modified during these few minutes before returning afterwards to the direct inclination angle. In this case, servo-controlling in real-time the orientation of the solar tracker on the optimum inclination angle would lead to displacing the solar tracker during these few minutes, for a gain which is certainly very little with regards to the electrical consumption of the actuator(s) and to the wear.